1. Field of the Invention
This invention relates to the field of propulsion systems for marine vessels, specifically to a propulsion system having a conical/tapered housing and a succession of increasingly smaller turbine/propeller blades each with a reduced pitch angle of between 10° and 12°, which is configured to propel a marine vessel by discharging fluid rearwardly with a thrust reaction of increased force that is approximately twenty percent greater than that produced by conventional propeller systems of comparable size. The wider end of the conical/tapered housing of the present invention, which is the suction side, is secured to the inside bottom surface of a marine vessel hull and has a bottom inlet opening aligned with an access hole through the hull, while the housing's opposing and narrowed discharge end is attached to the inside of the vessel's transom over a second hole. Preferably, an inlet opening cover plate with a keyhole-shaped opening is positioned flush within the outside bottom surface of the marine hull over its access hole, the keyhole shape being designed to disrupt the laminar flow of seawater under the hull and provide the inflow of a large volume of seawater through the inlet opening and into the wider end of the conical/tapered housing when the marine hull moves in a forwardly direction. For effective use, the narrow end of the keyhole-shaped opening must be placed in a position that faces the bow of the marine hull. Eddys form at the keyhole-shaped opening's rounded and tapering outside edges, which redirect the inertial energy of the seawater to flow upward into the conical/tapered housing at the center of the opening's leading edges, and the main flow of seawater to follow without protest. Due to the large amount of seawater induced by the keyhole-shaped opening to flow into the wider end of the conical/tapered housing, steam bubbles that are low in temperature and pressure are prevented from forming, and cavitation is eliminated as the seawater moves through the wider end of the conical/tapered housing toward the first propeller. Once drawn into the conical/tapered housing through the keyhole-shaped opening, the seawater is then directed across the succession of increasingly smaller turbine/propeller blades and discharged from the narrow end of the housing with increased thrust. The reduced pitch angle of each propeller blade, to a maximum that is between approximately 10° and 12°, further increases the efficiency of the present invention marine reaction thruster by creating a reduction in outgassing and cavitation as the seawater moves across the propeller blades. A reverse and steering assembly attached to the outside surface of the transom, and aligned with the discharge opening of the present invention, has a movable gate that controls the direction of forward/reverse movement of the associated marine hull. However, it is the speed of the inboard engine, which determines the velocity of the marine vessel associated with the present invention. When the gate is fully opened, the discharged seawater moves rearwardly through the reverse and steering assembly and the marine vessel moves in a forwardly direction. Correspondingly, when the gate is lowered, rearward movement of the seawater discharged from the conical/tapered housing and moving through the reverse and steering assembly is blocked, and the lowered gate instead forces all or a portion of the discharged seawater into a downward and forwardly direction under the marine vessel, which causes the vessel to stall or move in reverse. Rudders are also positioned within the reverse and steering assembly, and have Ackerman geometry to enhance the efficiency of making turns. Also, although the reverse and steering assembly runs best when it is above water, it still can be used effectively under water in surface and submarine vessels. Further, since each of the propeller blades positioned for rotation within the present invention's conical/tapered housing substantially fills its cross-sectional dimension, the propeller blade in the wider end of the conical/tapered housing necessarily has the largest diameter dimension and the propeller blade closest to the transom has the smallest diameter dimension. A debris-cutting member is preferably positioned in front of each propeller, and also preferably in front of the strut supporting the drive shaft upon which the propellers are mounted, to cut up pieces of seaweed, rope, and other debris in the seawater entering the conical/tapered housing that would otherwise accumulate into propeller-slowing clogs, as well as elongated strands of seaweed and/or other matter that would have a tendency to wrap itself around the propellers and/or strut and reduce thrust reaction efficiency. Size is not a limiting factor and the present invention marine reaction thruster can be enlarged or reduced in size during manufacture for varying applications. However, should the keyhole-shaped opening be sufficiently increased in size to place humans and large marine life at risk for being sucked into the conical/tapered housing during present invention use, safety precautions dictate that a grate and/or other appropriately configured means be secured across the inlet opening in a way that prevents large objects from entering the conical/tapered housing while at the same time continues to allow a large volume of seawater to enter it. Since the propulsion system of the present invention is enclosed within a marine hull and discharges fluid directly through a rear opening in its transom, its operation is virtually silent. In addition, the internal positioning of the present invention within the marine hull prevents propeller damage that might otherwise occur from contact with reefs, sandbars, and other underwater obstacles. Further, since no transmission is required, manufacturing cost is reduced. Recreational, commercial, and military applications are contemplated for both submarine and surface vessels.
2. Description of the Related Art
Standard drives for boats have certain disadvantages. For example, standard inboard engines have a tendency for excessive propeller slippage due to the angular geometry of their propeller installation, which worsens when the bow rises. When the pitch angle of a propeller becomes excessive, cavitation sets in and its operating efficiency is reduced. Standard outboard marine engines also have a similar excessive propeller pitch angle disadvantage, needed to compensate for their inability to accommodate large propellers. An excessive pitch angle in a propeller causes its blades to move faster through water than the water can close in behind them. This causes a vacuum to occur in the fluid flowing around the blades, and saturated steam is generated. The resulting cavitation and outgassing have a negative impact on the propeller's operating efficiency. Thus, current inboard and outboard marine propellers lose approximately thirty to forty percent of their operating efficiency as a result of the pitch angle of their blades being higher than needed. In contrast, the present invention propulsion system is designed to propel fluid by discharging it rearward beyond the transom of an associated marine vessel with a reaction of increased force that is approximately twenty percent greater than that created by conventional propeller systems of comparable size used in marine applications. The present invention is compact in configuration, has a conical/tapered housing, and preferably has a water inlet opening on its suction side with a keyhole-shaped configuration designed to induce a large volume of seawater into the wider end of the conical/tapered housing without cavitation. Further, the propeller blades of the present invention have increasingly smaller diameter dimensions that are successively positioned within the conical/tapered housing, and all are directly connected to an inboard motor via a common drive shaft. To avoid stalling of its propeller blades and prevent cavitation, each propeller has a maximum pitch angle between approximately 10° and 12°. As a result, since the volume of fluid moving across each successively smaller propeller blade is constant and each next smaller propeller must move more cubic inches of seawater per revolution than its adjacent larger propeller, the velocity of the seawater moving through the conical/tapered housing is successively increased and a thrust reaction is generated. A reverse and steering assembly aligned with the discharge opening of the conical/tapered housing has a movable gate that can be positioned to direct fluid discharged by the housing in a downward and forwardly direction under the associated marine vessel hull to provide it with reverse motion, while two crescent-shaped rudders each of semi-tubular design and located aft of the discharge opening provide steering for the marine vessel by laterally deflecting the discharged fluid after it exits the conical/tapered housing. Since the conical/tapered housing is located inside a marine hull, its propellers are protected from exterior damage, such as that due to contact with a reef or sandbar. The hull protection also prevents the propellers from causing injury to humans and large marine life, such as porpoises and manatees. Further, since the suction side of the present invention is through the bottom portion of the marine hull, it is always below water level and priming is never required. Also, no transmission is needed with present invention use. Thus, the present invention has many features and advantages not taught by the prior art, which assist the present invention in creating enhanced marine vessel operation.